JP6189659B2 - Antifogging agent and antifogging film - Google Patents

Description

  The present invention relates to an antifogging agent comprising anion-modified cellulose nanofibers, and also relates to an antifogging film in which a coating layer containing anion-modified cellulose nanofibers is provided on the surface of a film substrate.

  Films made of thermoplastic resins such as polyolefins such as polyethylene and polypropylene, polyvinyl chloride, ethylene / vinyl acetate copolymers, polyesters, polyamides, etc., take advantage of their superior properties to make food, pharmaceuticals, industrial parts, miscellaneous goods, etc. It is used for applications such as packaging materials and agricultural films. However, since the surfaces of these films are hydrophobic in nature, when they are placed in a high humidity environment, water droplets may form on the surfaces and the surfaces may become cloudy. For example, when used for film packaging for fruits and vegetables, lids for lunch boxes, etc., moisture from the food inside will cause water droplets on the surface of the film, causing the surface to become cloudy and the visibility will deteriorate, causing the food inside to be damaged. It may be difficult to see. In addition, when used in an agricultural house or the like, there is a problem that water droplets attached to the surface of the film block sunlight and adversely affect the growth of crops.

  In order to solve these problems, a surfactant called a drip agent or an antifogging agent is kneaded into the film and then molded, or applied to the surface of the molded film to improve the antifogging property. Giving is performed (Patent Documents 1 and 2).

JP 2008-50492 A JP 2006-299213 A

  In a film with antifogging properties, the antifogging agent bleeds out on the film surface and the surface is whitened to reduce transparency, or the surface is antifogged by being rubbed during use. In some cases, the effect may be reduced. An object of the present invention is to provide an antifogging agent that can provide a film that is less likely to lose its antifogging property and has excellent transparency, and an antifogging film using the same.

As a result of intensive studies on the above problems, the present inventors applied a coating comprising an anion-modified cellulose nanofiber having an extremely fine fibrous structure, and is excellent in antifogging and transparency, Further, the present inventors have found that the antifogging effect is not easily lost even by an external force such as friction. Although this invention is not limited to the following, it is as follows.
(1) An antifogging agent comprising an anion-modified cellulose nanofiber having an average fiber width of 1-1000 nm and an average fiber length of 50-5000 nm.
(2) In the above (1), the anion-modified cellulose nanofiber is a cellulose nanofiber introduced with a carboxymethyl group, and the degree of carboxymethyl substitution per glucose unit of cellulose is 0.01 to 0.50. Antifogging agent as described.
(3) The anion-modified cellulose nanofiber is a cellulose nanofiber introduced with a carboxyl group, and the amount of the carboxyl group is 0.5 mmol / g with respect to the absolute dry mass of the cellulose nanofiber introduced with a carboxyl group. The antifogging agent according to (1) above, which is -2.0 mmol / g.
(4) An antifogging film formed by providing a coating layer containing the antifogging agent according to any one of (1) to (3) on the surface of a film-like substrate.
(5) The antifogging film according to (4), wherein the film-like substrate is a polyolefin resin film or a polyester resin film.

  The present invention provides a novel antifogging agent comprising anion-modified cellulose nanofibers. By using the antifogging agent of the present invention, it is possible to provide an antifogging film that is excellent in antifogging properties and transparency and is not easily lost by an external force such as friction.

Hereinafter, the present invention will be described in detail. In the present specification, “to” includes values at both ends.
1. Anion-modified cellulose nanofiber <cellulose nanofiber>
In the present invention, the cellulose nanofiber refers to an extremely fine fiber that can be obtained by defibrating a cellulose raw material. In the present invention, in particular, cellulose nanofibers having an average fiber length of 50 to 5000 nm and an average fiber width of 1 to 1000 nm are used. Cellulose nanofibers having an extremely fine fiber form are fine, so that the dispersion has high transparency and can be suitably used as an antifogging agent that does not deteriorate visibility. Moreover, since it is fine, its specific surface area is large and its ability to absorb water vapor due to hydrophilic groups on the surface is high, so it can provide high antifogging properties. Furthermore, since it has a fiber form, the surface strength when the film is formed is increased, and it is less likely to be damaged when subjected to external force such as friction, and the antifogging property is not easily lost. .

<Cellulose raw material>
The cellulose raw material used as the raw material for cellulose nanofibers is typically kraft pulp or sulfite pulp derived from wood, and a high-speed rotating type, colloid mill type, high-pressure type, roll mill type, ultrasonic type dispersing device, etc. And wet high pressure or ultra high pressure homogenizer, powdered cellulose refined with a mill, or the like, or microcrystalline cellulose powder purified by chemical treatment such as acid hydrolysis, etc. Those derived from plants other than wood such as hemp, rice, bacus, and bamboo can also be used. When a large amount of lignin remains in the cellulose raw material, there is a risk of inhibiting the anion-modifying reaction of the cellulose raw material, which will be described later. Therefore, in the present invention, the cellulose raw material with a small amount of lignin obtained by the chemical pulp production method is used as an anion It is preferably used for modification. In order to further remove lignin, the cellulose raw material may be subjected to a known bleaching treatment.

<Anion modification of cellulose raw material>
The cellulose raw material is anion-modified before being converted into nanofibers. Anionic modification includes carboxymethylation or carboxylation of cellulose. Among these, carboxymethylated cellulose is known to have high safety, and can be preferably used particularly for food packaging.

(1) Carboxymethylation Using the above cellulose raw material as a starting material, 3 to 20 times by weight lower alcohol as a solvent, specifically methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, Add a medium such as tertiary butanol alone or a mixture of two or more and water. The mixing ratio of the lower alcohol is 60 to 95% by weight. As a mercerizing agent, 0.5 to 20 times moles of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide is added per glucose residue of the bottoming material. A bottoming raw material, a solvent, and a mercerizing agent are mixed and subjected to mercerization treatment at a reaction temperature of 0 to 70 ° C., preferably 10 to 60 ° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times mol per glucose residue, a reaction temperature of 30 to 90 ° C., preferably 40 to 80 ° C., and a reaction time of 30 minutes to 10 hours, preferably 1 hour. Perform etherification reaction for ~ 4 hours.

  In the present invention, it is preferable to use a carboxymethylated cellulose having a degree of carboxymethyl substitution per glucose unit of 0.01 to 0.50. By introducing a carboxymethyl substituent into cellulose, the celluloses repel each other electrically, so that the cellulose introduced with the carboxymethyl substituent can be easily fibrillated into nanofibers. When the carboxymethyl substituent per glucose unit is smaller than 0.01, the fiber cannot be sufficiently defibrated. On the other hand, when the carboxymethyl substituent per glucose unit is larger than 0.50, the fiber shape cannot be maintained because it swells or dissolves and may not be obtained as a nanofiber.

The degree of carboxymethyl substitution can be measured by the following method:
About 2.0 g of sample is precisely weighed and placed in a 300 ml stoppered Erlenmeyer flask. Add 100 ml of nitric acid methanol (1 ml of anhydrous methanol and 100 ml of special concentrated nitric acid) and shake for 3 hours to convert sodium carboxymethyl cellulose (Na-CMC) to carboxymethyl cellulose (H-CMC). The absolute dry H-CMC 1.5-2.0 g is precisely weighed and put into a 300 ml stoppered Erlenmeyer flask. Wet H-CMC with 15 ml of 80% methanol, add 100 ml of 0.1 N NaOH and shake at room temperature for 3 hours. Excess NaOH is back titrated with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator. Calculate the degree of carboxymethyl substitution using the following formula:
[{100 × F ′ − (0.1N H ₂ SO ₄ (ml)) × F} / (absolute dry mass of H-CMC (g))] × 0.1 = A
Carboxymethyl substitution degree = 0.162A / (1-0.058A)
A: Amount of 1N NaOH required to neutralize 1 g H-CMC (ml)
F ′: Factor of 0.1 N H ₂ SO ₄ F: Factor of 0.1 N NaOH (2) Carboxylation The cellulose raw material is composed of an N-oxyl compound and bromide, iodide or a mixture thereof. Cellulose introduced with a carboxyl group (hereinafter also referred to as “carboxylated cellulose” or “oxidized cellulose”) can be obtained by oxidizing in water using an oxidizing agent in the presence of a compound selected from the group. .

  The N-oxyl compound refers to a compound that can generate a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it promotes the target oxidation reaction. For example, the compound shown by the following general formula (Formula 1) is mentioned.

(In Formula 1, R1 to R4 represent the same or different alkyl groups having about 1 to 4 carbon atoms.)
Of the substances represented by Formula 1, 2,2,6,6-tetramethyl-1-piperidine-oxy radical (hereinafter referred to as TEMPO) is preferable. Further, the N-oxyl compound represented by any one of the following formulas 2 to 5, that is, the hydroxyl group of 4-hydroxy TEMPO was etherified with alcohol or esterified with carboxylic acid or sulfonic acid to impart moderate hydrophobicity. A 4-hydroxy TEMPO derivative or 4-acetamido TEMPO having an appropriate hydrophobicity by acetylating the amino group of 4-amino TEMPO is preferable because it is inexpensive and can provide uniform oxidized cellulose.

(In formulas 2 to 5, R is a linear or branched carbon chain having 4 or less carbon atoms.)
Furthermore, an N-oxyl compound represented by the following formula 6, that is, an azaadamantane-type nitroxy radical, is preferable because it can efficiently oxidize a cellulose raw material in a short time and is less likely to break a cellulose chain.

(In Formula 6, R ₅ and R ₆ represent the same or different hydrogen or a C _{1 to} C ₆ linear or branched alkyl group.)
The amount of the N-oxyl compound used is not particularly limited as long as it is a catalyst amount capable of converting the cellulose raw material into nanofibers. For example, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.05 to 0.5 mmol is more preferable with respect to 1 g of the absolutely dry cellulose raw material.

  Bromide is a compound containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Further, an iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, preferably from 0.1 to 100 mmol, more preferably from 0.1 to 10 mmol, and even more preferably from 0.5 to 5 mmol, with respect to 1 g of an absolutely dry cellulose raw material.

  As the oxidizing agent, known ones can be used, and for example, halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, peroxide and the like can be used. Of these, sodium hypochlorite is preferable because it is inexpensive and has a low environmental impact. The appropriate amount of the oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, still more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol with respect to 1 g of the absolutely dry cellulose raw material. preferable.

  The cellulose oxidation process allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature may be a room temperature of about 15 to 30 ° C. As the reaction proceeds, a carboxyl group is generated in the cellulose, so that the pH of the reaction solution is reduced. In order to advance the oxidation reaction efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11. The reaction medium is preferably water because it is easy to handle and hardly causes side reactions.

  The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually 0.5 to 6 hours, for example, about 0.5 to 4 hours.

  The oxidation reaction may be performed in two stages. For example, oxidized cellulose obtained by filtration after the completion of the first stage reaction is oxidized again under the same or different reaction conditions, so that the cellulose is not subject to reaction inhibition by the salt produced as a by-product in the first stage reaction. A carboxyl group can be efficiently introduced into the system raw material.

  In addition, the cellulose raw material may be appropriately subjected to alkali treatment before the oxidation step to change the crystal form to the II type. Ordinary cellulose is a type I crystal, but if it contains a type II crystal, the oxidant easily enters and the reaction efficiency is improved.

  It is preferable to set conditions so that the amount of carboxyl groups of oxidized cellulose is 0.5 to 2.0 mmol / g with respect to the absolute dry mass of cellulose. The amount of the carboxyl group can be adjusted by adjusting the oxidation reaction time, adjusting the oxidation reaction temperature, adjusting the pH during the oxidation reaction, adjusting the addition amount of the N-oxyl compound, bromide, iodide, or oxidizing agent.

  The obtained oxidized cellulose is preferably washed.

The amount of carboxyl groups can be measured by the following method:
Prepare 60 ml of 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose, add 0.1 M hydrochloric acid aqueous solution to pH 2.5, then add 0.05 N sodium hydroxide aqueous solution dropwise to adjust pH to 11. The electrical conductivity is measured until it is, and is calculated from the amount of sodium hydroxide (a) consumed in the weak acid neutralization stage where the change in electrical conductivity is slow, using the following formula:
Carboxyl group amount [mmol / g oxidized cellulose or cellulose nanofiber] = a [ml] × 0.05 / oxidized cellulose mass [g].

<Nanofiberization of anion-modified cellulose>
A dispersion containing the anion-modified cellulose obtained above is prepared, and the anion-modified cellulose is fibrillated in the dispersion to form nanofibers. “To make nanofiber” means to fibrillate cellulose to form a fine fiber having a nano-order fiber width. In the present invention, the anion-modified cellulose is processed into anion-modified cellulose fibers having an average fiber width of 1 to 1000 nm, preferably 2 to 150 nm, and an average fiber length of 50 to 5000 nm, preferably 100 to 5000 nm. The dispersion medium of the dispersion is preferably water from the viewpoint of ease of handling.

  In order to disentangle anion-modified cellulose and disperse it in a dispersion medium, a strong shearing force is applied to the dispersion using a high-speed rotating type, colloid mill type, high pressure type, roll mill type, ultrasonic type device, etc. It is preferable. In particular, in order to efficiently obtain anion-modified cellulose nanofibers, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer capable of applying a pressure of 50 MPa or more to the dispersion and applying a strong shearing force. The pressure is more preferably 100 MPa or more, and further preferably 140 MPa or more. By this treatment, the anion-modified cellulose is fibrillated to form anion-modified cellulose nanofibers, and the anion-modified cellulose nanofibers are dispersed in the dispersion medium.

  The concentration of the anion-modified cellulose in the dispersion used for the treatment is 0.1% (w / v) or more, preferably 1 to 50% (w / v), and 1 to 10% (w / v). More preferred. It may be 2 to 10% (w / v), or 3 to 10% (w / v).

2. Antifogging agent The antifogging agent of the present invention comprises an average fiber width of 1 to 1000 nm (preferably 2 to 150 nm) and an average fiber length of 50 to 5000 nm (preferably 100 to 5000 nm) obtained by the above method. The anion-modified cellulose nanofibers having such ultrafine fiber form are highly transparent when used as a dispersion or film, and have a large specific surface area, so they have the ability to absorb water vapor. High and has excellent antifogging properties. Moreover, since it is fibrous, when it is set as a film | membrane, it has the advantage that it is hard to damage with respect to external forces, such as friction.

  The antifogging agent of the present invention can impart antifogging properties to a substrate by coating on a substrate such as a film and forming a coating film on the surface of the substrate.

  Conventionally, in order to improve the gas barrier properties of the film, it has been proposed to use cellulose nanofibers as an inner layer of a laminated film to form a gas barrier film, but cellulose nanofibers are applied to the outermost surface of a substrate, It has never been proposed to use it as an agent for preventing water droplets from forming on the surface of the substrate (giving antifogging properties to the substrate). The present invention is the first use of cellulose nanofiber as an agent for imparting antifogging properties to a substrate.

3. Coating to base material When applying the anti-fogging agent of the present invention to a base material, various additions are made to anion-modified cellulose nanofibers depending on the type of base material to be used, as long as the desired effect is not impaired. An agent can be added. Typically, various additives are mixed in a dispersion of anion-modified cellulose nanofibers to prepare a coating solution. For example, when a hydrophobic film is used as a substrate, the leveling property and antifoaming property of the coating liquid are improved by adding an organic solvent such as isopropyl alcohol and a surface conditioner such as acetylene glycol and silicon compound. In order to lower the viscosity of the coating solution, it is also possible to add an ionic compound such as sodium chloride or sodium acrylate. Moreover, it is also possible to add a crosslinking agent for imparting water resistance to the coating film. For these additives, it is desirable to use highly safe materials for use in food packaging materials and agricultural materials. The concentration of the anion-modified cellulose nanofiber in the coating solution is not particularly limited. Various additives may be added as long as the dispersibility of the anion-modified cellulose nanofibers is not significantly impaired.

The method for coating the substrate is not particularly limited, and a known method can be used. The coating amount of the base material is not particularly limited, based on the weight of the anionically modified cellulose nanofibers is about ^{0.01~10g / m 2, 0.1~5g / m} 2 approximately, more preferably I will.

  In the present invention, since the main purpose is to prevent water droplets from forming on the surface of the substrate (giving antifogging properties), at least the coating layer containing the antifogging agent is usually at least the outermost surface of the substrate. Apply as follows. Depending on the application, the coating may be on one side or both sides of the substrate, or may be part of the surface.

  Examples of a preferable substrate on which the antifogging agent of the present invention is applied include a film-like substrate made of a polymer compound, and a plate-like substrate such as acrylic, polycarbonate, reinforced plastic, and glass. Among them, a highly transparent base material is preferable. For example, a film having a transparency measured as a total light transmittance of 80% or more, preferably 85% or more can be used. Examples of the transparent polymer compound film include polyolefin resin films such as polyethylene film and polypropylene film, polyester resin films such as polyethylene terephthalate film, and polyamide resin films such as nylon film. It is not something. Further, the thickness is not particularly limited. The thickness may be a thickness generally called a film, for example, about 10 to 1000 μm. These films may be unstretched or may be stretched films such as uniaxial and biaxial in the longitudinal and lateral directions.

4). Anti-fogging film The film obtained by applying the anti-fogging agent of the present invention can be used for various applications as an anti-fogging film. For example, it can be used as a packaging material for food and the like, or an agricultural film. In this case, normally, at least the coating layer containing the antifogging agent of the present invention is on the side where water droplets are considered to be attached (for example, the side facing the food when used for packaging materials such as food). Used to face.

  The antifogging film of the present invention only needs to have a coating layer containing an antifogging agent on at least one side (or a part thereof). In this case, by providing an adhesive layer or the like on the surface that does not have the coating layer of the antifogging agent, it can also be used by being attached to another substrate.

  The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

<Measurement of transparency of anion-modified cellulose nanofiber dispersion>
The cellulose nanofiber dispersion was diluted to 0.1% with water, and the transparency was measured as UV light transmittance using a UV-VIS spectrophotometer UV-265FS (Shimadzu Corporation).

<Evaluation of antifogging property of film>
About 100 ml of hot water (90 ° C.) was poured into a 200 ml beaker, and the film was placed in a beaker so that the coated surface of the resulting laminated film was on the hot water side and steamed for 30 seconds, and then the visibility of the film was confirmed. .

<Measurement of average fiber length and average fiber width>
The cellulose nanofiber fixed on the mica section was observed with a scanning probe microscope (manufactured by Hitachi High-Tech Science Co., Ltd.) (3000 nm × 3000 nm), and the fiber width for 20 fibers was measured to calculate the average fiber width. The average fiber length was calculated from the obtained observation image using image analysis software WinROOF (Mitani Corporation).

<Friction resistance test>
Using a Gakushin dyeing fastness tester (manufactured by Suga Test Instruments Co., Ltd.), the change in anti-fogging property after one reciprocation of the surface on the coating layer side of the laminated film with a cloth wetted with water was evaluated. When the antifogging property is reduced by this operation, it is considered that the external force such as friction is weak, and when the antifogging property does not change, the external force such as friction is considered strong.

[Example 1]
(Production of carboxymethylated cellulose)
To a stirrer capable of mixing pulp, add 200 g of pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) and 440 g of sodium hydroxide in dry mass, and add water so that the pulp solid concentration is 15%. It was. Then, after stirring for 30 minutes at 30 ° C., the temperature was raised to 70 ° C., and 585 g (in terms of active ingredient) of sodium monochloroacetate was added. After reacting for 1 hour, the reaction product was taken out, neutralized and washed to obtain carboxymethylated cellulose having a carboxymethyl substitution degree of 0.24 per glucose unit.

(Preparation of carboxymethylated cellulose nanofiber dispersion)
The carboxymethylated cellulose was adjusted to 1.0% (w / v) with water and treated 10 times with an ultrahigh pressure homogenizer (20 ° C., 140 Mpa) to obtain an anion-modified cellulose nanofiber dispersion. The transparency of the obtained dispersion was 99%, the average fiber length was 860 nm, and the average fiber width was 26 nm.

(Creation of laminated film)
After adding 20 parts by weight of isopropyl alcohol to 80 parts by weight of the dispersion, a polypropylene film subjected to corona treatment (0.25 kW) (DIFAREN P2160T thickness 25 μm: manufactured by DIC, total light transmittance 92% ) Using an applicator, the anion-modified cellulose nanofibers after drying were coated and dried so that the coating amount was 0.5 g / m ² to obtain a laminated film having a total light transmittance of 91%. The resulting laminated film had a film surface that was not clouded with steam, was kept transparent, and had good visibility. Further, when the above-mentioned friction resistance test was conducted, no decrease in antifogging property was observed.

[Example 2]
Example except that sodium hydroxide was 264 g in absolute dry weight, 351 g of sodium monochloroacetate was used, and the coated substrate film was a polyester film (DIFAREN E7800 PET, thickness 30 μm: manufactured by DIC, total light transmittance 92%) In the same manner as in Example 1, an anion-modified (carboxymethylated) cellulose nanofiber dispersion and a laminated film coated therewith were prepared. The degree of carboxymethyl substitution of the obtained carboxymethylated cellulose is 0.15, the transparency of the nanofiber dispersion is 99%, the average fiber length is 986 nm, the average fiber width is 38 nm, and the total light transmittance of the laminated film Was 90%. In the evaluation of antifogging properties, the film surface was not fogged with steam, transparency was maintained, and visibility was good. In the friction test, no decrease in antifogging property was observed.

[Example 3]
An anion-modified (carboxymethylated) cellulose nanofiber dispersion and a laminated film coated with the same were prepared in the same manner as in Example 1 except that sodium hydroxide was 88 g by dry weight and sodium monochloroacetate was 117 g. did. The degree of carboxymethyl substitution of the obtained carboxymethylated cellulose is 0.05, the transparency of the nanofiber dispersion is 97%, the average fiber length is 1210 nm, the average fiber width is 65 nm, and the total light transmittance of the laminated film Was 88%. In the evaluation of antifogging properties, the film surface was not fogged with steam, transparency was maintained, and visibility was good. In the friction test, no decrease in antifogging property was observed.

[Example 4]
(Production of carboxylated (oxidized) cellulose)
Add 500 g of bleached unbeaten kraft pulp (whiteness 85%) derived from coniferous trees (absolutely dry) to 500 ml of an aqueous solution in which 780 mg of TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide are dissolved, until the pulp is uniformly dispersed Stir. An aqueous sodium hypochlorite solution was added to the reaction system to 6.0 mmol / g to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but a 3M sodium hydroxide aqueous solution was sequentially added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system no longer changed. The reaction mixture was filtered through a glass filter to separate the pulp, and the pulp was sufficiently washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g.

(Preparation of carboxylated cellulose nanofiber dispersion and creation of laminated film)
A nanofiber dispersion and a laminated film were prepared in the same manner as in Example 1 except that the oxidized pulp obtained in the above step was used. The transparency of the obtained dispersion was 99%, the average fiber length was 350 nm, the average fiber width was 4 nm, and the total light transmittance of the laminated film was 91%. In the evaluation of antifogging properties, the film surface was not fogged with steam, transparency was maintained, and visibility was good. In the friction test, no decrease in antifogging property was observed.

[Comparative Example 1]
The antifogging property of the polypropylene film was evaluated in the same manner as in Example 1 except that the cellulose nanofiber dispersion was not applied. The film surface was clouded with steam, and visibility was deteriorated.

[Comparative Example 2]
A carboxymethyl cellulose powder having a carboxymethyl group substitution degree of 0.74 (trade name: APP-84, manufactured by Nippon Paper Chemicals Co., Ltd.) (not fibrous) is diluted to a concentration of 10% to a mixer. A laminated film was obtained in the same manner as in Example 1 except that the coating solution was prepared by dissolving by the above. In the evaluation of anti-fogging property, the film surface was not fogged with steam and the transparency was maintained and the visibility was good. However, in the friction resistance test, the anti-fogging property was reduced.

  The results are shown in Table 1.

Claims (6)

The average fiber width 1 to 1,000 nm, and a anionically modified cellulose nanofibers is the average fiber length of 50 to 5000 nm, proof that the counter ion of the anionic group comprises an anion-modified cellulose nanofibers is ^{H +} or Na ⁺ Clouding agent.   The antifogging according to claim 1, wherein the anion-modified cellulose nanofiber is a cellulose nanofiber having a carboxymethyl group introduced therein, and the degree of carboxymethyl substitution per glucose unit of the cellulose is 0.01 to 0.50. Agent.   The anion-modified cellulose nanofiber is a cellulose nanofiber introduced with a carboxyl group, and the amount of the carboxyl group is 0.5 mmol / g to 2. with respect to the absolutely dry mass of the cellulose nanofiber introduced with the carboxyl group. The antifogging agent according to claim 1, which is 0 mmol / g. The counter ion is Na ⁺ The antifogging agent according to any one of claims 1 to 3, wherein The film for anti-fogging formed by providing the coating layer containing the anti-fogging agent of any one of Claims 1-4 on the surface of a film-form base material. The film for anti-fogging according to claim 5 , wherein the film-like substrate is a polyolefin resin film or a polyester resin film.